Refer to: EN 15614 Para 8.4.3 Joint variables, AWS D1.1: WPS variables – Joint design, ASME IX: WPS variables – Joint design.

5.4 Essential Variables
5.4.1 General
A welding procedure shall be reestablished as a new welding procedure specification and shall be completely requalified when any of the essential variables listed in 5.4.2 are changed. Changes other than those given in 5.4.2 may be made in the procedure without the need for requalification, provided the welding procedure specification is revised to show the changes.

5.3.2.4 Joint Design description in WPS
The specification shall include a sketch or sketches of the joint that show the angle of the bevel, the size of the root face, and the root opening or space between abutting members. The shape and size of fillet welds shall be shown. If backing is used, the type shall be designated.

5.4.2.3 Joint Design Essential variable
A major change in joint design (e.g. from V groove to U groove) constitutes an essential variable. Minor changes in the angle of bevel or the land of the welding groove are not essential variables.